Fuse having vibration damping means for protecting the fuse link thereof

ABSTRACT

A cartridge-type current limiting fuse is provided with a mechanical damping means for mounting a fusible link in the fuse in a manner such that the link will be protected from damage due to mechanical vibration of the equipment on which it is mounted during normal operating use.

[22] Filed:

United States Patent Vrabelet al.

[54] FUSE HAVING VIBRATION DAMPING MEANS FOR PROTECTING TI-IE FUSE LINK THEREOF [72] Inventors: Edward A. Vrabel; Raymond Cuzzone, both of Pittsfield, Mass.

[73] Assignee: General Electric Company Oct. 7, 1971 [211 Appl. No.: 187,450

[52] US. Cl. ..337/246, 337/158, 337/204 [51] Int. Cl. ..Il0lh 85/14 [58] Field oi Search ..337/l59, 202, 204, 229, 231,

[56] References Cited UNITED STATES PATENTS 1,152,147 8/1915 Davis... ..337'/204 x 1451 Oct. 17, 1972 3,256,409 6/1966 Brandt ..337/276 X 3,294,935 12/1966 Leonard et a1 ..337/204 X 3,465,275 9/1969 Swain ..337/l5 8 X Primary Examiner--Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney-Francis X. Doyle et al.

[57] ABSTRACT A cartridge-type current limiting fuse is provided with a mechanical damping means for mounting a fusible link in the fuse in a manner such that the link will be protected from damage due to mechanical vibration of the equipment on which it is mounted during normal operating use.

9 Claims, 4 Drawing Figures FUSE HAVING VIBRATION DAMPING MEANS FOR PROTECTING THE FUSE LINK THEREOF BACKGROUND OF THE INVENTION The invention described herein relates to high voltage fuses of a type adapted to interrupt over-load current surges or short circuit currents. More specifically,

ing on the systems to which the transformers are connected. It is common practice in mounting fuses in such distribution transformers to insert the fuse into an oilfilled transformer tank through an insulating bushing mounted on the tank. This kind of fuse mounting arrangement makes it possible to easily withdraw the fuse from its operating position within the transformer, so that the fuse can be replaced after its fuse link has melted. One consequence of such fuse mounting arrangements in the elongated bodies of transformer bushings is that a relatively long electrical connection is required between the ends of the fuse cartridge, even though only a short fuse link is needed to afford the desired interrupting capability. Such a long electrical connection has been found to present a significant problem in suitably mounting the fuse element so that it is adequately protected from damage resulting from vibration of the fuse link and the elongated conductor connected to it within the fuse housing.

it is well known in the prior art to construct various types of current limiting fuses with structural features that enable the fuses to sustain severe thermal cycling without being damaged. Thermal cycling is particularly severe in fuses used to protect large motors or other loads that require wide ranges of current magnitude, due to frequent starting, running and stopping operations for the motors. The resultant large changes in load current produce major mechanical stresses on protective fuse links, due to the thermal cycling of these links. Accordingly, it is a well known practice to design fuse links for such current limiting fuses with bowed portions along the length of the fuse link. These bowed, or bent, portions provide longitudinal flexibility for the fuse links so that thermal cycling of the fuse can be easily adsorbed in the flexible portions of the fuse link, without resulting in metal fatigue, which might break the link and thus render it unserviceable. One example of such a prior art current limiting fuse having elongated fusible links that are bent, or bowed, at spaced-apart points is shown in US. Pat. No. 3,400,235, which issued Sept. 3, 1968 and is titled Current Limiting Fuse. This patent is assigned to the assignee of the present invention.

In addition to the known prior art fuse structures which provide bowed or bent fuse links to protect the fuse against damage due to thermal cycling, it is a common practice in the fuse art to bend or bow fuse links,

. over substantially their entire length, in order to mount a relatively long fuse link within a shorter cylindrical housing. in general, such fuse links are either helically formed or are bent into a zigzag configuration. Such prior art fuse link mounting arrangements ordinarily do not incorporate any means for damping the movement of the link in a direction transverse to its longitudinal axis. An example of such a prior art fuse link mounting arrangement is shown in US. Pat. No. 3,287,524 titled,

Sand-Teflon Means to Improve Low Current Interruption Performance of High Voltage Current Limiting Type Fuses, which issued Nov. 22, 1966 and is assigned to Joslyn Manufacturing and Supply Co., of Chicago, Illinois.

The present invention differs from the type of prior art bent or bowed fuse links described above, both in function an in structure. Fuses constructed pursuant to the teaching of the present invention will include a generally straight fuse link that is electrically coupled to, and mechanically supported by, a conductor form ed of less flexible material. This supporting conductor is bowed or bent at spaced-apart points along its length in a manner such that it cooperates with the fuse housing to dampen movement of the fuse link in a direction transverse to its longitudinal axis. Thus, the present invention is not directed primarily toward solving the problems inherent in thermal cycling of fuse links, or toward the problem of mounting a relatively long fuse link within a short fuse housing. Instead, the present invention affords a desirable solution to the problem of mechanical fatigue of fuse links due to prolonged vibration of these links during their normal operating use in distribution transformers or other electrical apparatus. Those familiar with the problems inherent in providing suitable fuse protection for distribution transformers realize that in recent years, as harder steels have been employed to manufacture transformer tanks, the mechanical vibration to which transformer fuses has been subjected has increased. Such increased fuse vibration is due to the ability of such relatively harder steels to better transmit to the fuse mounting bushing the small vibrations induced in the tank by the normal Hertz hum caused by the magnetic forces present in a transformer. A further increase in the fuse vibration problem stems from the relatively thinner steel walls that are being used on present-day distribution transformers, as more corrosion resistant steels and organic coatings are used to make transformer tanks.

Accordingly, it is a primary object of the present invention to provide a fuse that includes means for mechanically damping the movement of its fusible link with respect to its mountings, thereby to protect the fuse link against damage due to mechanical vibration.

Another object of the invention is to provide an optimum means for mounting a relatively short fuse link in a substantially longer insulating housing in a manner such that the fuse link is spaced from the inner walls of the housing but at the same time is protected from mechanical fatigue due to vibration of the fuse during its normal usage.

A further object of the invention is to provide a fuse with a mechanical damping means that limits the range of movement of a fuse link transverse to its longitudinal axis within predetermined limits. I

Yet another object of the invention is to provide an electrical transformer protective fuse that is economical to manufacture and maintain while at the same time affording the foregoing objectives in the environment of mechanical fuse mounting vibrations present in an energized power distribution transformer.

Additional objects and advantages of the invention will be apparent to those skilled in the art from the description of the invention presented herein below.

SUMMARY OF THE INVENTION In one preferred form of the invention, a high voltage fuse of a type suitable for protecting a distribution transformer in an underground electric power distribution system is formed by electrically connecting a short fuse link in series with a less flexible electrical conductor formed of twisted wires. The fuse link and seriesconnected conductor are mounted in a hollow cylindrical passageway formed by a cylindrically-shaped insulating fuse housing. The respective opposite ends of the conductor and fuse link are electrically connected to suitable fuse terminal caps mounted in sealed relationship on the opposite ends of the fuse housing. In accordance with the present invention, a small diameter hollow insulating cylinder of paper or other suitable material is positioned around the fuse link, and a packing element, such as a cylinder of corrugated paper, is mounted between the cylinder and the fuse housing to limit the range of movement of the fuse link in a direction transverse to its longitudinal axis. Also, the elongated, twisted-wire conductor that is connected to the fuse link is bent or bowed at spaced-apart points along its length so that it contacts the inner walls of the fuse housing at spaced-apart points. This novel configuration of the fuse link supporting conductor serves to further dampen the transverse movement of the fuse link with respect to its longitudinal axis. The novel combination of mechanical damping means thus afforded serves to prevent the fuse link from being damaged by mechanical stresses induced in it by the type of vibrations encountered when the fuse is mounted in operating position within a transformer and is subjected to the 60 Hertz vibration induced in the transformer tank from the windings of the transformer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view, partly in cross section, showing a high voltage fuse that incorporates a fuse link damping means constructed pursuant to the teaching of the invention.

FIG. 2 is a top plan view, in cross section, taken along the plane 2-2 of FIG. 1. This view of a fuse constructed pursuant to the invention illustrates one form of the damping means of the invention, which is positioned around the fuse link of the fuse illustrated in FIG. 1.

F iG. 3 is a top plan view, in cross section, taken along the plane 3-3 of FIG. 1, illustrating one position of an elongated conductor, which is shown in FIG. 1 as being connected in series with the fuse link of the fuse depicted in the Figure.

FIG. 4 is a side elevation view, in cross section, of a portion of the fuse shown in FIG. 1. The portion of the fuse shown in FIG. 4 illustrates in enlarged detail some features of the damping arrangement of the present invention, at the junction of the fuse link and elongated conductor shown in the fuse of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, it will be seen that there is shown a high voltage fuse 1 of a type that is suited for use in the protective circuit of a distribution transformer. The illustrated fuse includes an insulating housing 2 which isgenerally cylindrical in shape and is formed of a conventional pressed organic insulating material. Of course, other types of conventional insulating materials may be used to form the housing 2 in other embodiments of the invention. As seen in FIG. 1, wall means 3 define a passageway 3' through the housing 2 from one end to the other end thereof. A pair of electrical terminals 4 and 5 are mounted respectively on opposite ends of the housing 2. The terminal 4 is in the form of a cup-shaped metal cap that is sealed in a suitable manner over the upper end of the fuse l. The terminal 5 includes a threaded stud portion 5a and a threaded insert portion 5b that is adapted to be screwed into threads formed in the walls of passage 3, as shown, to seal the lower end of the fuse l.

A relatively flexible fuse link 6 in the form of a low melting point metal wire is brazed to one end of an electrical conductor 7 at the end 7a thereof. The electrical conductor 7 in this embodiment of the invention is formed of a plurality of twisted wire strands so that it is thicker and substantially less flexible than the fuse link 6. In this embodiment of the invention, the diameter of conductor 7 is preferably at least twice as thick as the diameter of the fusible link 6'so that the end 7a of conductor 7 is rigidly supported in its central position with respect to the passageway 3. Moreover, it will be understood that the diameter of fuse link 6 is preferably in the range of 0.02 inch to 0.1 inch in order to be properly supported in its operating position by the dampening means 10. The upper end of the fuse link 6 is connected by a suitable coupling means 6a to the terminal 4. In this embodiment, coupling means 6a comprises a solder that secures link 6 to terminal 4. The bottom end'of conductor 7 is connected in any suitable manner, such as by soldering it, to a central bore in the threaded insert portion 5b of terminal 5 so that an electrical circuit is formed between terminals 4 and 5 by link 6 and conductor 7 extending through the passageway 3'.

Pursuant to a major feature of the present invention, the electrical conductor 7 is formed intermediate its ends to define a plurality of bends 8, 8a, and 8b therein. These bends are effective to contact the wall means 3 of passageway 3' thereby to limit the movement of the conductor 7 transverse to its longitudinal axis to a predetermined range of movement that is defined by the spacing between the conductor 7 and wall means 3; operating in connection with the inherent flexibility of the conductor 7. By thus limiting the transverse movement of conductor 7, the movement of the end thereof which supports one end of fuse link 6 is significantly dampened so that the movement of fuse link 6 is likewise dampened. It has been found that good results are obtained if the bend 8 is spaced less than 1% inches from the end 7a of conductor 7, when the conductor 7 is formed of strands of copper wire and is approximately one-sixteenth inch thick. Moreover, for best results, at least three bends, such as bends 8, 8a, and 8b, should be used, because if only one or two bends are employed, there is a tendency for the end 7a of conductor 7 to be pivoted around the bend so that, it can be vibrated by movement of the remainder of its body length.

It will be noted that in FIG. 1 the conductor 7 is depicted as being covered over an intermediate portion of its length, including the bends 8, 8a, and 8b, with a coating of insulating material 9. In this form of the invention, the coating of insulating material 9 extends over a major portion of the length of the conductor 7 and is held in contact with the wall means 3 of passageway 3 by the bends 8, 8a, and 8b in the conductor 7. Thus, in this preferred embodiment of the invention, the limited range of transverse movement allowed to the upper end 70 of conductor 7 is constrained by the resilience of the coating material 9 and the flexibility of conductor 7. It will be understood that the coating of insulating material 9 may be formed of any suitable electrical insulating material such as a thermosetting plastic, or an electrical insulating fabric material.

A second major feature of the invention is the provision in the fuse l of a vibration damping means 10 that is effective to afford unrestricted movement of the fuse link 6 within a first range of movement transverse to its longitudinal axis, while being further effective to dampen movement of the link 6 in a second range of its movement transverse to its longitudinal axis. The vibration damping means 10in the preferred embodiment of the invention being described comprises a hollow cylinder 11 (also seen in FIG. 2) of insulating material, which is mounted around the fuse link 6 and is substantially coextensive with the length of the fuse link. As shown in FIG. 1, one end of the cylinder 11 abuts the coating of insulating material 9 on conductor 7. The other end of the cylinder 11 abuts the inner surface of terminal cap 4 adjacent the coupling means 6a thereon that are used to fasten the link 6 to terminal 4. In combination with the insulating cylinder 11, there is provided a flexible packing 12, in the form of a generally cylindrically shaped piece of corrugated insulating material, such as paper. The corrugations in the flexible packing 12 are best seen in FIG. 2.

It will be appreciated by examining FIG. 2 that fuse link 6 is free to vibrate within a first limited range of movement transverse to its longitudinal axis, which is defined by the inner surfaces of the cylinder 11. In addition, the fuse link 6 may vibrate in a second range of movement that is defined by the movement afforded to the cylinder 11 by the flexibility of the corrugated flexible packing 12. This combined damping means 10 serves to appreciably restrict, and cushion, the mechanical stresses applied to the fuse link 6 during its normal usage on a transformer, which subjects the fuse l to considerable vibration.

The foregoing description of a preferred embodiment of the invention should enable those skilled in the art to practice the invention. However, some additional features of the preferred embodiment will be explained in greater detail in order to assure a complete understanding of the invention. Accordingly, it should be noted that the upper end 7a of conductor 7 is positioned substantially adjacent the center of the passageway 3' in spaced-apart relation with respect to the wall means 3 thereof. This relationship is shown in greater detail in FIG. 4 of the drawing. Consequently, there is no undesirable mechanical loading of the end of the flexible packing 12 by the inherent resilience of the conductor 7, since conductor 7 is biased to its central position by the location of the bends 8 and 8a therein. As best seen in FIG. 4, the end 7a of conductor 7 is brazed or soldered to one end of the fuse link 6. It will be understood that although the fuse link 6 is generally straight, during normal manufacturing handling, it will frequently be bent so that it may contact the sides of the cylinder 11 at several points. Such contact only serves to further limit the possible transverse movement of the fuse link 6 and thus further aids in the vibration damping effect of the dampening means 10.

Of course, those skilled in the art will appreciate that alternative embodiments of the invention may be developed and various modifications may be made in the disclosed embodiment of the invention without departing from the true scope of the invention. It is our in tention to define the scope of the invention in the claims appended hereto.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A fuse comprising an elongated insulating housing, wall means defining a passageway through said housing, a pair of electrical terminals mounted on said housing, respectively, adjacent opposite ends thereof, an elongated, flexible fusible link, said link being substan tially shorter than said housing, an electrical conductor electrically connected in series with said link, one end of said conductor being connected to said link to form an electrical circuit therewith through said passageway, between said terminals, vibration damping means mounted between said link and said housing, said vibration damping means being effective to afford unrestricted movement of said fuse link within a first range of movement transverse to its longitudinal axis while being further effective to dampen movement of said link in a second range of its movement transverse to the longitudinal axis thereof, coupling means for coupling the other end of said conductor in fixed relationship to one of said terminals, said conductor being formed intermediate its ends to define a plurality of bends therein, said bends being effective to contact the wall means defining said passageway thereby to limit the movement of said conductor transverse to its longitudinal axis to a predetermined range of movement, whereby the movement of said one end of the conductor and the link connected thereto is further dampened.

2. An invention as defined in claim 1 wherein the other end of said conductor is positioned adjacent the center of said passageway, in spaced-apart relationship with respect to the wall means thereof.

3. An invention as defined in claim 2 wherein said conductor is at least twice as thick in diameter as said fusible link.

4. An invention as defined in claim 3 wherein said fusible link is generally uniform in diameter and its diameter is in the range of .02 inch to 0.1 inch.

5. An invention as defined in claim 1 wherein said vibration damping means comprises a hollow cylinder of insulating material mounted around said link and substantially co-extensive with the length thereof, in combination with a flexible packing positioned between the hollow cylinder and the wall means of said passageway.

6. An invention as defined in claim 5 wherein said flexible packing comprises a generally cylindricallyshaped piece of corrugated insulating material.

7. An invention as defined in claim 5 including a coating of insulating material mounted on said conductor over a major portion of the length thereof, said coating being held in contact with the wall means of said passageway by the bends in said conductor.

8. An invention as defined in claim 1 wherein said plurality of bends comprises at least three bends (8, 8a, and 8b). 5

9. An invention as defined in claim 8 wherein the one of said bends positioned closest to the fusible link is within one and one-half inches of said link. 

1. A fuse comprising an elongated insulating housing, wall means defining a passageway through said housing, a pair of electrical terminals mounted on said housing, respectively, adjacent opposite ends thereof, an elongated, flexible fusible link, said link being substantially shorter than said housing, an electrical conductor electrically connected in series with said link, one end of said conductor being connected to said link to form an electrical circuit therewith through said passageway, between said terminals, vibration damping means mounted between said link and said housing, said vibration damping means being effective to afford unrestricted movement of said fuse link within a first range of movement transverse to its longitudinal axis while being further effective to dampen movement of said link in a second range of its movement transverse to the longitudinal axis thereof, coupling means for coupling the other end of said conductor in fixed relationship to one of said terminals, said conductor being formed intermediate its ends to define a plurality of bends therein, said bends being effective to contact thE wall means defining said passageway thereby to limit the movement of said conductor transverse to its longitudinal axis to a predetermined range of movement, whereby the movement of said one end of the conductor and the link connected thereto is further dampened.
 2. An invention as defined in claim 1 wherein the other end of said conductor is positioned adjacent the center of said passageway, in spaced-apart relationship with respect to the wall means thereof.
 3. An invention as defined in claim 2 wherein said conductor is at least twice as thick in diameter as said fusible link.
 4. An invention as defined in claim 3 wherein said fusible link is generally uniform in diameter and its diameter is in the range of .02 inch to 0.1 inch.
 5. An invention as defined in claim 1 wherein said vibration damping means comprises a hollow cylinder of insulating material mounted around said link and substantially co-extensive with the length thereof, in combination with a flexible packing positioned between the hollow cylinder and the wall means of said passageway.
 6. An invention as defined in claim 5 wherein said flexible packing comprises a generally cylindrically-shaped piece of corrugated insulating material.
 7. An invention as defined in claim 5 including a coating of insulating material mounted on said conductor over a major portion of the length thereof, said coating being held in contact with the wall means of said passageway by the bends in said conductor.
 8. An invention as defined in claim 1 wherein said plurality of bends comprises at least three bends (8, 8a, and 8b).
 9. An invention as defined in claim 8 wherein the one of said bends positioned closest to the fusible link is within one and one-half inches of said link. 